From the patent application WO 8703626 A1 is known a plant for producing nonwoven web of fibres by air laying the fibres by means of a forming head. The fibres are by a fan transported from a defibrator to the forming head via a conduit.
The main current form the defibrator to the forming head is passing a screen for separating nits from acceptable fibres.
Therefore, the screen needs to have very large dimensions for being able to treat such large quantities of material. The invested capital in a plant of WO 8703626 A1 therefore of necessary will be rather high.
Also, the process of this known plant is uneconomical because the large quantities of energy, which need to be used for driving the main current through the large screen for only separating the few percent of nits in the main current.
The quality of the resulting product from a plant according to WO 8703626 A1 also will be poor as the nits in this plant are separated from a large current having a low percent of nits, as in D1.
Moreover, it is not possible to obtain a product which is essential free from nits when trying to separate nits in the main current, as nits afterwards are produced during the pneumatic transport to the forming head and during the process in this.
When separation the nits from the main stream not only nits are separated but also well-opened fibres are separated and that in a quantity, which will be much larger than the quantity of the separated nits. These separated well opened fibres are together with the separated nits returned to the defibrator subjecting this to heavy load. As the defibrator normally is the bottleneck of the plant said draw back results in that the difibrator need to be dimensioned with an oversize. That means that the plant of D1 also by this reason will be more costly in investment and more costly to operate than a similar plant according to the present invention.
Furthermore, the well-opened fibres, which are returned to the defibrator will be shortened whereby the fibre product will obtain a poor quality.